Marijuana and the Adolescent Brain

More and more states are legalizing marijuana for medical and recreational use. Researchers, doctors, educators, and parents are taking note and need to fully understand the health effects of cannabis use in minors.

You and your teen should consider these new research findings:

  • com and U.S. News and World Report released a 2018 survey that found 2.1 million middle and high school students have engaged in vaping marijuana.
  • Researchers in Europe found that marijuana can increase the amount of gray matter in a teenager’s brain, which affects adolescent development.
  • A new study in the Journal of Neuroscience found that after just one use of marijuana, the teenage brain can be altered.

We do know that marijuana can slow a person’s reaction time, make their heart race, and affect short-term memory. But what else might it do, especially to developing adolescent brains?

In one study, researchers scanned the brains of 46 14-year-olds from Ireland, England, France, and Germany. They found that those who used marijuana had higher brain volumes than those who didn’t. Specifically, brain volume referred to increased gray matter, a mass of cells that affect how humans mature over time.

Here’s why this matters. At age 14, the median age of the teens in the study, “Teens’ cortical regions go through a process of thinning or pruning,” says the lead author of the study and a professor of psychiatry. However, when marijuana was introduced, the increased amount of gray matter “disrupted this pruning process” which, in turn, interrupted the normal maturation process. But how much, or to what end, we don’t yet fully understand.

In addition to changing the teenage brain, marijuana also has other effects on the human body:

  • Tetrahydrocannabinol, better known as THC, is the main psychoactive component in marijuana. THC reacts with the body’s cannabinoid receptors resulting in slower reaction times to stimuli.
  • The National Institute on Drug Abuse has shown that marijuana can make a user’s heart rate temporarily jump. This feeling may last between 20 minutes and three hours and can cause a heart rate increase of up to 50 beats per minute. Since a usual resting heart rate is 60 bpm, this rate is nearly double the average.
  • Marijuana users may also experience issues with their short-term memory loss, since the THC affects how a brain processes information, according to a 2013 study.

Compounding all these verifiable health issues is what behavioral psychologists have long known about adolescent brains. That is, because the frontal cortex of their brains is still developing, adolescents are much more likely to engage in risky and experimental behavior. Additionally, vaping (rather than smoking) marijuana is seen as a cooler, more accepted way to get high. Plus, weed is now more readily accessible (often legal for those 21 years and older) across America and elsewhere.

Parents and their teens should take notice. Although we have research showing that marijuana affects the brain in some limited long- and short-term ways, we simply do not yet know what the long-term outlook is for teens who smoke or vape marijuana on an ongoing basis.

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